Use Input-output Redirection

General Information

Using input/output redirection (>, », |, 2>, etc.).

Redirect standard output to a file, overwrite contents

cat /etc/system-release > info.txt

Redirect standard output to file, append to file

tail /etc/passwd >> info.txt

cat /etc/passwd | wc -l

• Counts the number of lines in /etc/passwd

2> Redirect standard error

ssh admin@webserver01.com "uptime" 2>/dev/null

• SSH to webserver01.com, issue the uptime command, send standard errors to /dev/null (to nowhere)

Redirect both standard error and standard output

ssh admin@webserver01.com "uptime" &> results.log

Redirect standard error to standard out

cat /etc/system-release /etc/Red 2>&1 | grep Red

• Standard output can be passed through a pipe to the next command. By redirecting standard error to standard output, any error messages are successfully sent through as well.